After all search engines produced their individual lists, they are
merged into a single list. In meta-search, this process is known
as a ranking aggregation function [1]}.
Aggregation functions can be classified into two main types [2]}:
(i) those that use similarity scores returned by the search engine,
and (ii) those that use ranking positions. When engines do not
expose their similarity scores for their results, as in the
cases of Google or Bing, ranking positions can be used instead.
For this reason, we decided to use Borda Fuse in our approach. Borda Fuse is a positional aggregation function that is computationally simple to implement [1]}, and it performs well in the context of Web searching [4]}.
